Hitherto, as a structure for constituting a casing of projection television, an example disclosed in Japanese Laid-open Patent No. 5-130541 has been known. In this disclosed projection television, a cathode-ray tube (CRT) and a circuit board compose a CRT block. This CRT block can be separated from the mirror, screen, and cabinet. Thus, the CRT block can be mounted easily on the cabinet.
As an electromagnetic impedance countermeasure structure of electronic appliance, an example is disclosed in Japanese Laid-open Patent No. 7-183684. In the disclosed structure of shield plate, both sides of a shield plate having a conductor are fixed inside of an upper case by a pi-shaped protrusion provided inside of the upper case. Further, the shield plate, lower case, and grounding terminal of printed board of logic circuit are fastened with screw at the same position. Thus, the shield structure capable of preventing effects of static electricity or noise is obtained.
Recently, as the frequency is becoming higher in integrated circuit (IC) board of circuit unit, resistance to electromagnetic impedance is further demanded in projection television and other electronic appliances. It is hence more and more needed to reinforce the shield by metal casing or the like. On the other hand, as the screw tightening portions and shielding components are increasing in number, service tends to be more and more difficult.
In the case of projection television, further, even an optical clearance may cause to lower the electromagnetic shielding performance or pass undesired reflected light.